I am interested in building a basic beamforming circuit to explore the concept. I would like to be able to change the signal acquisition direction through adjusting mic output delays.

I'm sure there are somewhat comprehensive sources on this subject (and have searched the posting archives here for beamforming), but I haven't found them.

Some questions:
Are there any basic mic array circuits and/or documented builds suitable for this purpose that the community could point me toward?
Would filtering the mics to a typical voice 30-3400hz band improve or degrade system performance?
How many mics would be necessary to get a minimum degree of performance?

 

Hello,

Perhaps the follwing pages from ESP might interest you:
http://sound.westhost.com/articles/microphones.htm
http://sound.westhost.com/project93.htm

Bertus

 

I built an ultrasonic beamformer (http://interestingto.me.uk/Open Source/adventures-ultsasonics) and found quite a lot of resources on line. Mine is a bit simpler than yours and the beam forming is on transmit rather than receive but the principal is the same. Also the principal is the same whether acoustic or RF so web sites with details for radio beam forming can be used.

Start here - http://en.wikipedia.org/wiki/Beamforming

 

Thanks for those links, they are helpful background on mics and I will keep them at hand.

I'm really trying to learn more specifically about arrays and beamforming implementation.

 

Thank you for the pointers Sirch2...and a very interesting project.

I'll try to incorporate the transmission side of things into my thought process. I'm not sure how yours would necessarily be simpler than what I'm trying to do: at this point, I imagine I will just start with 3 mics and see where I get. I'll take a look through the refs at the wikipedia article. So far the lab site (http://www.labbookpages.co.uk/audio/beamforming/delaySum.html) looks most useful for implementation advice.

I built an ultrasonic beamformer (http://interestingto.me.uk/Open%20Source/adventures-ultsasonics) and found quite a lot of resources on line. Mine is a bit simpler than yours and the beam forming is on transmit rather than receive but the principal is the same. Also the principal is the same whether acoustic or RF so web sites with details for radio beam forming can be used.

Start here - http://en.wikipedia.org/wiki/Beamforming

 

Hello,

If you want the microphone be very directional, you could use a parabolic reflector.
On this page of the EDYCYPEDIA you will find some links how to build and use them:
http://educypedia.karadimov.info/electronics/microphonestypes.htm

Bertus

 

Hi Bertus,

A parabolic reflector would work with a single fixed direction. However, I'm interested in handling varying directions and sources in a stationary fashion. From my understanding, I think a set of variable delay functions would be best suited, though I'm certainly open to other options. Particularly as I'm not sure yet how I'd implement the variable delays.

Hello,

If you want the microphone be very directional, you could use a parabolic reflector.
On this page of the EDYCYPEDIA you will find some links how to build and use them:
http://educypedia.karadimov.info/electronics/microphonestypes.htm

Bertus

 

Hello,

Perhaps the following page might interst you:
http://research.microsoft.com/en-us/projects/microphone_array/

Bertus

 

I don't think 3 mics is going to do very much because in one dimension you effectively only have one mic. The seven in my arrangement was about a few as is sensible and got the beam angle down to about 11° IIRC. You woiuld be better off with a grid of 9.

I found a really good on-line calculator that would compute shape, beam angle, etc. but I can't find it now

 

Thanks for that insight Sirch2.

I'm looking at an implementation (essentially a conference table or other circle of sources) with sources in the range of 1-4 meters spread around 360 degrees. So, I wouldn't be assuming a parallel wavefront, and was thinking about a triangular mic arrangement, which would actually exploit that a little. Do you think even at proof of concept level that wouldn't work? I guess to get to 9 I need to pass through 3...so, might as well start and see.

I'll google around for the calculator you mention.

I don't think 3 mics is going to do very much because in one dimension you effectively only have one mic. The seven in my arrangement was about a few as is sensible and got the beam angle down to about 11° IIRC. You woiuld be better off with a grid of 9.

I found a really good on-line calculator that would compute shape, beam angle, etc. but I can't find it now